Method for improving the dyeability of fiber-forming cellulose esters



United States Patent 3,006,830 METHOD FOR IMPROVING THE DYEABILITY 0FFIBER-FORMING CELLULOSE ESTERS Lamar C. Cloninger, Midland, andFrederick M. Arnesen, Bay City, Mich., assignors to The Dow ChemicalCompany, Midland, Mich, a corporation of Delaware Filed May 31, 1957,Ser. No. 662,908 9 Claims. (Cl. 204154) When conventional dyeingprocedures are employed, the conventionally available types of celluloseacetate and other cellulose esters of the fiber-forming variety,including cellulose propionate, cellulose butyrate and the like andmixtures thereof can only be dyed with the type of dyestufis or coloringagents that are of the dispersed acetate class of material. It would bean advantage to enhance the dye-receptivity of fiber-forming celluloseacetate and the like cellulose ester composition in order to render themsusceptible to being easily and satisfactorily colored with a greaterdiversity of dyestuffs and coloring agents.

The chief aim and concern of the present invention, therefore, is toprovide an improved and highly effective method for increasing thedyeability of various shaped or preformed articles, particularlyfilamentous structures of various fiber-forming cellulose esters,especially cellulose acetate, to permit their being readily dyed,particularly by acid and direct types of dyestufis. The invention alsorelates and has for an object the provision of fiber-forming celluloseester compositions, particular cellulose acetate compositions, havingpronounced receptivity of the indicated and other varities of dyestufisin addition to those that belong to the dispersed acetate class.

According to the present invention, a shaped article, particularly afilamentary shaped or preformed article, of fiber-forming celluloseacetate or other of the fiberforrning cellulose esters mayadvantageously be treated for improvement of its dyeability withoutappreciably altering or deleteriously influencing the physicalproperties of the cellulose ester by a method which comprises firstthoroughly impregnating at least the surface of the shaped article beingtreated with a sulfonated alkenyl aromatic monomer (as, for example,with a sulfonated styrene monomer such as styrene sulfonic acid or itssalts) then subsequently exposing the intimately mixed cellulosesubstrate and sulfonated monomer impregnant thereof to a field of highenergy radiation to efiiciently provide an effectively attached graftcopolymer of the polymerized sulfonated alkenyl aromatic monomericimp-regnant on the cellulose ester substrate. The resulting product isgenerally found to be readily and easily dyeable to deep and levelshades of coloration using acid and direct types of dyestufis whileemploying conventional techniques for their application. In addition,the graft copolymer modified product of the invention is oftentimesfound to also be quite readily dyeable with other varieties of dyestuffsthat conventional cellulose esters do not normally accept to anypronounced degree, such as the vat, sulphur and napthol types of dyes.The desirable physical properties and characteristics of the celluloseester substrate are not adversely affected by treatment or modificationin accordance with the present invention. In many cases, the modifiedcellulose ester substrate of the present invention, especially when itis dyed with either acid or direct type colors, may be found to havesuperior fastness properties to an unmodified cellulose acetate or otherfiber-forming cellulose ester that has been dyed according toconventional procedures with a dispersed acetate type of dyestufi. Animproved filamentary cellulose ester article that has been modified inaccordance with the present invention is schematically illustrated inthe sole figure of the hereto annexed drawing.

3,006,830 Patented Oct. 31, 1961 The quantity of sulfonated alkenylaromatic monomer that is intimately impregnated in the cellulose estersub strate for the high energy radiation-induced graft copolymerizationtherewith may not only depend upon the specific nature andcharacteristics of the particular substrate that is intended to bemodified as Well as the particular graft copolymerizing efiiciency ofthe sulfonated monomeric impregnant that is involved, but also upon thedegree of modification that may be desired to be imparted in theresulting composition. Generally, the quantity of the monomer that isemployed should be adequate to secure the desired enhancement of thedyeability or dyereceptivity of the cellulose ester substrate to acidand direct type of dyestuffs.

Ordinarily a satisfactory result may be achieved when minor proportionsof the sulfonated monomer are thoroughly impregnated in the polymersubstrate that is intended to be modified. In some instances, very minorproportions may suffice, especially when low levels of acid and directtype dye-attracting improvement are satisfactory for a particularpurpose at hand. Broadly speaking, it is desirable to employ such aquantity of the monomer that may be adapted to provide an average ofbetween about 1 and 30 percent by weight of grafted dye-receptivepolymerized sulfonated monomer on the cellulose ester chain that isdesired to be modified. To the attainment of such ends, it mayfrequently be found advantageous to impregnate in or to incorporate withthe cellulose ester substrate an amount of the sulfonated monomericimpregnant that is between about 1 and percent by weight, based on theweight of the cellulose ester substrate. In some cases it may benecessary to achieve relatively higher impregnated quantities of thesulfonated monomer in a plurality of successive impregnating steps ortreatments. An amount of the sulfonated monomer that is between about 1and 30 percent by weight may be even more advantageous for most purposeswithin the contemplation of the present invention. This is for thereason that the relatively greater receptivity to acid and direct typesof dyes that may be obtained by utilization of greater relativeproportions of the monomer is frequently unnecessary for practicalpurposes. In this connection, as has been indicated, it is mostdesirable for as large a proportion as possible (preferably all orsubstantially all) of the sulfonated monomer to result in a graftcopolymer that is firmly attached to the cellulose ester substrate.Thus, it is beneficial for the application of the radiation to becontinued until from 1 to 30 percent by weight and preferably from 1 to15 percent by weight (which is more than adequate for most practicalpurposes), of the graft copolymer is obtained on the cellulose estersubstrate (based on the weight of the latter) to insure the desiredincrease in specific dye-receptivity.

The sulfonated alkenyl aromatic monomer may be intimately impregnated inor incorporated with the cellulose ester substrate in any desired mannerprior to mutual irradiation of the associated, graft copolymerizablemixture. Thus, the monomer may be directly applied to or mixed orblended with the cellulose ester substrate or it may be applied fromdispersion or solution in suitable liquid vehicles until a desiredmonomer content has been obtained. In many instances it may be anadvantage to apply the monomer from aqueous solution having aconcentration that is at or near saturation. In this connection, thecellulose ester substrate may be modified while it is in either afabricated or unfabricated condition. Usually, however, it is moreexpedient to modify already fabricated shaped articles of the substratesuch as filaments, fibers, films or other shaped or molded structures.

The sulfonated alkenyl aromatic monomers that may able mixture orcombination of materials.

be employed in the practice of the present invention are of the typehaving the general formula:

wherein R is'selected from the group consisting of hydrogen and methyl,AI is an aromatic radical (including nuclear substituted aromaticradicals) containing from 6 to 10 carbon atoms, n has a value of and 1and X is selected from the group consisting of hydrogen and alkalimetals. Advantageously, the sulfonated alkenyl aromatic monomer isarranged with the sulfonate substituent in a position that is para tothe alkenyl group. Sulfonated alkenyl aromatic monomers that may beemployed suitably in the practice of the invention include sulfonatedstyrene monomers, sulfonated vinyl toluene monomers, sulfonated vinylxylene monomers, sulfonated vinyl naphthalene monomers and vinyl benzylsulfonates. Preferably, as indicated, sodium styrene sulfonate orstyrene sulfonic acid are employed as the sulfonated alkenyl aromaticmonomers in the practice of the present invention.

The high energy radiation which is utilized for inducing the graftcopolymerization in the sulfonated monomer/ cellulose ester mixtures isof the type which provides emitted particles or photons having anintrinsic energy of a magnitude which is greater than the planetaryelectron binding energies which occur in the graft copolymeriz- Suchhigh energy radiation is conveniently available from various radioactivesubstances which provide beta or gamma radiation as, for example,radioactive cobalt, nuclear reaction fission products and the like. Ifit is preferred, however, high energy radiation from such sources aselectron beam generators, X-ray generators and the like may also beutilized. It is beneficial to employ the high energy radiation in afield of at least about 40,000 roentgens per hour (or equivalentionizing potency) intensity. A roentgen, as is commonly understood, isthe amount of high energy radiation as may be provided in a radiationfield which produces in one cubic centimeter of air at a temperature of0 C. under 760 millimeters of absolute mercury pressure such a degree ofconductivity that one electrostatic unit of charge is measured atsaturation (when the secondary electrons are fully utilized and the walleffect of the chamber is avoided).

It is most desirable to graft copolymerize all of the sulfonatedmonomeric impregnant to and with the cellulose ester substrate whilethemixture is being subjected to the influence of the mutual high energyradiation. Room temperatures may be employed satisfactorily forirradiation although elevated temperatures may also be utilized. Thepreferred radiation dosage in million roentgen equivalent physicals(mrep.) that is employed is in an amount or quantity that is adapted toquickly accomplish the graft copolymerization without deleteriouslyinfluencing or degrading the cellulose ester substrate. Generally, aradiation dosage between, say, about 0.25 and 10 mrep. may besatisfactorily employed. Oftentimes it may be more advantageous when thedosage that is utilized for affecting the desired graft copolymerizationis between about 0.5 and 5 mrep. Obviously, the greatest economy andadvantage may be achieved when minimum high energy radiation dosages areinvolved. Greatly excessive dosages should be assiduously avoided toavoid degradation of the reactants, especially after all orsubstantially all of the sulfonated alkenyl aromatic monomer has becomegraft copolymerized to the cellulose ether/substrate. After theradiation-induced graft copolymerization has been completelyaccomplished, it may oftentimes be desired to scour or otherwise purifythe modified cellulose ester product in order to ensure the removaltherefrom of any residual unreacted monomer (or even loosely associatedpolymer of the sulfonated monomer) that may'not have entered intochemical combination with the .substrateunder influence of the highenergy irradiation. a

In order to further illustrate the invention, about a 15 gram sample (ona dry weight basis) of a spun cellulose acetate yarn of about 242 denierwas wound on a glass test tube having an outside diameter of about 1.8centimeters. The wound yarn sample was then inserted in a larger testtube which contained an adequate quantity of a 10 percent by weightaqueous solution of sodium styrene sulfonate to cover the yarn. The yarnwas maintained in the solution until it had absorbed about 14.5 percentby weight of the sulfonated monomer, based on the dry weight of theyarn. While in the solution, the sample was exposed at room temperatureto a field of high energy radiation that was emitted from a cobalt 60source until a total dosage of about 4 mreps. had been effected. Themodified yarn was then scoured (using an aqueous scouring solution inthe conventional manner of about 0.5 percent by weight, based on theweight of the fiber, of a commonly employed anionic detergent) for 30minutes at a temperature of about 160 F. After having been scoured, theyarn was dyed in an aqueous dyebath that contained 2 percent by weight(based on the weight of the fiber) of well dissolved Wool Fast Blue BLA(an acid type dyestuff), 20 percent by weight of Glaubers salt, and 5percent by Weight of acetic acid (28 percent strength) having a liquorto fiber ratio of about 30:1. The yarn was admitted to the dyebath at atemperature of about 100 F., after which the temperature of the bath wasraised to 195-200 F. and maintained at the elevated temperature for 45minutes. After having been dyed, the yarn was removed from the dye bath,rinsed well with warm water and subsequently scoured for 15 minutes inthe above-indicated manner. It was found to have been become dyed to adeep and level shade of blue. The graft copolymerized fiber was found tohave picked up about 11.8 percent by weight of the grafted copolymer,based on its unmodified weight. The treated yarn had a tenacity of about0.70 gram per denier and an elongation of about 12 percent.

For purposes of contrast with the foregoing, an unmodified sample of thesame cellulose acetate yarn (which had a tenacity of about 0.75 gram perdenier and an elongation of about 8.8 percent) was attempted to be dyedin the same manner as above described. The unmodified yarn was onlystained to a very pale, relatively streaked, blue shade of coloration.For purposes of additional comparison, when a sample of the samecellulose acetate yarn was subjected to the same high energy dosageWithout being immersed in the sulfonated monomer solution, its tenacity(after irradiation) was found to have been diminished to about 0.51 gramper denier and its elongation to about 7.8 percent.

Similar excellent results were also obtained when the foregoingprocedure was repeated, excepting to replace the sodium styrenesulfonate monomer with the free acid form of the monomer and with sodiumvinyl benzyl sulfonate and to dye the graft copolymer modified yarn withsuch dyestuffs as are listed in the following tabulation, in which thecolor index (or American Prototype No., where appropriate) is givenalong with the identity of the manufacturer of each of the dyestuffs.

DIRECT DYES Name CI Company Diamine Fast Red FA-CL 419 GDO. DiamiueScarlet 3BACF 382 GDC. Fastusol Blue LR Pr. 443 GrDG. Calcomine AzurineBI onc 502 000. Benzo Green CA-CF 593 GDQ Fastusol Yellow RA Extr 349aGDC. Calcodur Orange EGL.-. B Pr. 72 000. Calcodur Yellow BL Con 814C00. Calcomine Blue R Conc Pr. 22 CCC. Calcomiue Chrome Brown BS Pr. 21C00. Pontarnine Violet N Cone. 150 percent 394 Du Pont s Benzo FastScarlet GSA-CF 326 GD C.

Indicates Prototype designation.

b General Dyestufi Corporation.

a American Cyanamid Company.

d Ciba Company, Inc.

2 El. du Pont de Nemours 6: 00., Inc.

Good results may also be obtained when the salt or free acid forms ofsulfonated vinyl toluene, sulfonated vinyl xylene and sulfonated vinylnapthaline monomers are employed in ways analogous to that illustratedwith sulfonated styrene monomer in the practice of the presentinvention.

What is claimed is:

1. A method for improving the receptivity to direct and acid typedyestuffs of shaped articles of fiber-forming cellulose esters whichcomprises thoroughly impregnating at least the surface of the shapedarticle with between about 1 and about 75 weight percent, based on theweight of the cellulose ester substrate, of a sulfonated alkenylaromatic monomer compound of the structure:

wherein R is selected from the group consisting of hydrogen and methyl,Ar is an aromatic radical having from 6 to 10 carbon atoms, n has avalue of 0 or 1, and X is selected from the group consisting of hydrogenand alkali metals; then subsequently exposing the intimately mixedcellulose ester substrate and sulfonated monomer impregnant thereof to afield of high energy radiation having a minimum intensity of about40,000 roentgens per hour which is applied until a dosage between about0.25 and 10 mreps. is efiected and at least a portion of the sulfonatedmonomer graft copolymerizes with the cellulose ester substrate.

2. The method of claim 1, wherein the shaped article is a filamentaryshaped article.

3. The method of claim 1, wherein the field of high energy irradiationhas a minimum intensity of about 4. The method of claim 1, whereinbetween about 1 and 30 percent by weight of the sulfonated monomer,based on the weight of the cellulose ester substrate, is impregnated insaid substrate.

5. A method according to the method set forth in claim 4, wherein theirradiation is continued until from 1 to 15 percent by weight of saidmonomer impregnant is chemically attached to said cellulose estersubstrate as dye-receptive graft copolymer pendages.

6. The method of claim 1, wherein said cellulose ester substrate iscellulose acetate.

7. The method of claim 1, wherein said sulfonated alkenyl aromaticmonomer is a sulfonated styrene mon orner.

8. The method of claim 1, wherein said sulfonated alkenyl aromaticmonomer is a Vinyl benzyl sulfonate monomer.

9. The method of claim 1, wherein said sulfonated alkenyl aromaticmonomer is a sulfonated vinyl toluene monomer.

References Cited in the tile of this patent UNITED STATES PATENTS2,053,819 Felix et al. Sept. 8, 1936 2,104,722 Bertsch Ian. 11, 19382,654,716 Sorenson Oct. 6, 1953 2,666,025 Nozaki Jan. 12, 1954 2,681,846Guthrie et al. June 22, 1954 2,763,609 Lewis et al Sept. 18, 19562,789,030 Fetscher Apr. 16, 1957 2,830,943 Mackenzie Apr. 15, 19582,839,479 Caldwell et al. June 17, 1958 FOREIGN PATENTS 1,130,100 FranceSept. 17, 1956 1,079,401 France Dec. 12, 1955 (4th Addition of No.66,034) 1,079,401 France May 19, 1954 750,923 Great Britain June 20,1956 OTHER REFERENCES Chen et al.: I. Poly. Sci. vol. 23, pages 903913,Feb. 1957.

Pinner et al.: Plastics, pages 27-3 0, J an. 1958.

Brookhaven National Laboratory Report No. 414, pp. 1-14, Oct. 1956.

Ballantine: Modern Plastics, pp. l71-176, Sept. 1957.

Quarterly Progress Report B.N.L. 367, cover, 27, 28, July 1-Sept. 30,1955, Brookhaven National Laboratory.

1. A METHOD FOR IMPROVING THE RECEPTIVITY TO DIRECT AND ACID TYPEDYESTUFFS OF SHAPED ARTICLES OF FIBER-FORMING CELLULOSE ESTERS WHICHCOMPRISES THOROUGHLY IMPREGNANTING AT LEAST THE SURFACE OF THE SHAPEDARTICLE WITH BETWEEN ABOUT 1 AND ABOUT 75 WEIGHT PRECENT, BASED ON THEWEIGHT OF THE CELLULOSE ESTER SUBSTRATE, OF A SULFONATED ALKENYLAROMATIC MONOMER COMPOUND OF THE STRUCTURE: